Adhesivity of asphalts to mineral aggregates



Patented a. 19, 1943 ADHESIVITY 0F ASPHALTS T0- MINERAL AGGBEGATES Joseph C. Boediger, Brooklyn, N. Y., assignor, by

mesne assignments,

to Standard Catalytic Company, a corporation of Delaware ivo Drawing. Application November 30; 1939,

Serial No. 306,855 a 1Claim. (01. 106-281) Thi invention relates to the coating of mineral aggregates with diflerent types of bituminous compositions whereby firm permanent bonds be tween the coatings and the aggregates are obtained with consequent increase in the lengths of the life of the finished products.

It has heretofore been required to dry mineral aggregates which are to be bonded by means of asphalts, especially where hot application procedures are followed as it is very diificult to obtain a uniform coating of the asphalt in the presence of water. On mixing a wet mineral aggregate and an untreated asphalt, stripping frequently occurs with the result that mineral aggregate is obtained which is only partially coated. This partially coated aggregate is easily stripped of the asphalt, especially if there is an early exposure to the action of water, that is; a heavy rainfall occurring shortly after the laying operation. Y

One of the objects of the p esent invention is to permit the coating of the aces of damp or wet ag r gates with a bituminous composition in such a manner that the coating obtained is satisfactory and produces a firmly bonded mass.

A further object of this invention is to prepare a paving mixture bonded with asphalt in which the asphalt coating when applied to either dry or wet aggregate is not readily displaced or stripped when subjected to the action of water.

Other objects of the invention will be readily understo on reading the following description of the in ention.

It has been proposed that wetting agents, such as heavy metal salts of fatty acids, naphthenic acids or sulfonic acids prepared in the refining of petroleum oils, be incorporated in an asphalt to increase the adhesivity. (i. e. resistance to displacement by water) and wetting power of the said asphalt. A substantial increase in the wetting power of asphalt and also in the adhesivity of the asphalt to the mineral aggregate is obtained by the addition of such heavy metal fatty acid salts, but if the mineral aggregate is wet, a satisfactory-asphalt coating is, not always obtained, that is, a coating that will satisfactorily cover the wet stone and also resist subsequent displacement by water. This wetting power and adhesivity vary according to the mineral aggregate on which the asphalt is applied. For example, it has been found that certain trap-rocks are not readily coated with treated asphalt when wet and the resulting coating, in any case, does not have suihcient adhesivity to .offer high resistance to subsequent stripping by the action of water.

According to this invention, when an aggregate tions, untreated asphalt when applied to dry a gregate will generally exhibit low resistance to stripping by water action and when applied to wet aggregate will generally fail to provide a satisfactory coating. Although the incorporation of a heavy metal salt into asphalt may permit the satisfactory coating of wet aggregate, lime pretreatment is often necessary to produce a coating of high adhesivity. This improvement in resistance to stripping by water action is especially noted when a wet or damp mineral aggregate is pretreated with 0.5 to 1% of hydrated lime prior to the application of the asphalt containing a metallic salt of a fatty acid.

The preliminary lime treating of mineral ag-. gregate is not detrimental in that it does not lessen the coating power of the asphalt or the adhesivity of the asphalt and the mineral aggregate. both the coating ability and the adhesivity properties of an asphalt that is applied to a limepretreated mineral aggregate even though an asphalt is used that readily coats the mineral gregate. The lime pretreatment of mineral aggregate may be used with any asphalt containing heavy metal salts that may be added as adhesivity promoters.

In the following table theeffects of lime pretreatment on adhesivity are illustrated. The stones used are obtained from the State of Virginia, except the last stone which was obtained in the State of New Jersey. The following procedure was used in evaluating the various mixtures:

The stone, graded to inch size, was drenched with distilled water and allowed to drain on a #10 mesh sieve for one minute.

The wet stone was transferred to a 16-ounce seamless tin can and 1% of V. M. 8: P. naphtha mixed with the wet stone. Following this, 6% of the-asphalt under test and at 375-400 F. was incorporated with the stone by stirring with a stiif knife. Vigorousmuxing was continued for There is generally some improvement in one minute. The resulting mix was evaluated as follows:

Mia: evaluation The per cent of aggregate surface coated with asphalt was visually estimated.

Adhesivity evaluation at 140 F.

After the mix was allowed to stand one hour at room temperature, it was placed in water maintained at 140 F. for 20 hours. At the completion of this period, the per cent of aggregate surface remaining coated with asphalt was deter- I mi nor MIXI G TESTS-VIRGINIA AGGREGATES Mrx FORMULA Dry or wet aggregate mixes maintained at 90 F. The breakdown of the track is taken as the number of revolutions of the machine required to loosen 300 lb. (10 per cent) of the total asphalt-aggregate mixture laid.

CI RCU'LAR TRACK TESTS The addition of lead naphthenate to the asphalt increased the life of the paving mixture whenmeasured by the number of revolutions the stone (dry or drenched) gm 200 wheels made around the circular track before V, M. 8; P. naphtha cc 2.5 failure of the track occurred. The rock used was 90/100 penetration asphalt added at tem- New Jersey trap-rock and a dry rock bonded with perature of 375 F gm 12 asphalt withstood over 6000 revolutions of the t l wheels around the circular track before failure,

Wet aggrega e p mmes while the same rock bonded with an asphalt con- Drenched stone ,gm 200 t ining 1% of lead naphthenate withstood more Hydrated lime gm 1 than twice as many revolutions of the wheels V. M. & P. naphtha cc 2.5 around the circular track. When the same rock 90/100 penetration asphalt added at tem was used wet and lime pretreated and then coated perature of 375 F gm 12 with asphalt it withstood over 8000 revolutions of Treatment in asphalt None 2.5% lead naphthenate 2.0% lead naphthennte Adhesiv- Adhesiv- Adhesiv- H of Condition MIX evalu- Mix evalu- Mix evalusource Eton) gtone of aggregate ation l 13%? ation 1 :62? ntion 1 132;

100 o s 95 so 100 90+ Gravel #1 (Richmond S. & G.) 6. 3 0 80 70/80 70 20 5/10 90 9o 80 30/40 100 o & 100 100 100 on Gravel (Wayncsboro stone) 7. 9 0 0 80 10 70 ll) 0 0 100 60/70 90 lo 100 5 100 100 100 100 Gravel #2 (Richmond S. & G.) 7. 8 0 0 80/90 /70 0/5 10/20 0 90 so 20 100 0/5 100 100 100 100 Granite (Trego stone) 8. 9 0/5 0/5 00 90 40 o/s 0 5 90+ 80 90 80 90 40 30 40 100 100 100 100 Granite (Sunnyside granite) 7. 2 40 80/90 90+ 80/90 70/150 40 5 -90 90 so so 100 o 100 we 100 100 Green trap rock (Charlottesville stone). 8. 4 at 0/5 0 70/80 20/30 40 20 Wet-lime" 0/5 0 90+ 90/100 90 70/80 Dry 100 0/5 100 100 100 80/90 Trap-rock, New Jersey 7. 5 Wet 0 70 5 20 0/5 Wet-lime 5/10 100 60/70 90 10/20 1 Mix evaluation-Per cent coated directly after mixing.

2 Per cent of aggregate surface still coated with asphalt. Aggregate cured 1 hour at room temperature, then placed in water for 20 hours at F.

The above tests were considered very drasticand in the following circular track tests, a laboratory method is devised which is very similar to that of actual road tests. A circular track was employed which consisted of a concrete trough 2 ft. wide and 16 ft. in mean diameter in which hot-mixed paving mixture is placed and then compacted by the machine. The machine consists of a centrally pivoted, mechanically rotated beam supporting at its end two truck Wheels equipped with heavy duty tires which have been loaded to give a dead weight of 1000 lb. on each tire. The linear speed of the wheels is 4.54 M. P. H. and they make seven passages from one side of the trough to the other each hour, to eliminate rutting. After suitable compaction followed by a curing period, the asphaltaggregate mixture is broken down by running the wheels over the track submerged under water 200 gm. New Jersey trap-rock wet with:

4 gm. water, then 1 gm. hydrated lime was added, followed by 3 cc. V. M. 8: P. naphtha containing the treatment and 11 gm, 90/100 penetration asphalt at 300 F.

1 Omitted in case of no line pretreatment tests.

These results show the eifectiveness to be obtained by using lime pretreatment on the aggregate when the agent is dissolved in the naphtha prime. The results also show the partial effectiveness of treatment with naphthenic acids which does not result in as high an adhesivity as was obtained with the sulfonate salts, but which may be suflicient in practice.

A cutback asphalt also may be used according to this invention, for example, R. C. type cutback,

prepared by the blending of approximately 25% of naphtha and 75% of 90/100 F. penetration asphalt of Venezuelan grade, after treatment with 1.5 and 2% of lead naphthenate by weight gave the following results when applied to wet trapasphalt, untreated or treated with lead naphthenate, was satisfactorily coated when the wet stone was pretreated with lime and the asphalt.

contained both lead naphthenate and naphthenic acids.

Con-me Ann-1r? or Ho'r Asrnsnr 0N Lima Panrnmrnn War Gmnrrn Per cent of e te Treatment in asphalt coated In addition, the ability of the resultant asphalt coating on the wet stone to resist displacement by water (i. e. adhesivity), even at elevated temperatures, is greatly increased, viz:

. Aonnsrvrry or AsrnAL'r To War, Lms Paarn narnn Gaamrn Aceaacsrr:

Y Adhesivity Treatment on asphalt at R Ncne 0 2.6 lead naphthenate 10 2.5 0 lead naphthenate and 2.0% naphthenic acids 80 The suggested method of treatment is thererock: fore of decided advantage in the field when wet i'i t ft i t t Per cent on Lime Coated on 5 a A ent d A r ate Condition room temdis iaeement g use cutback gg 6g per cent mixing pemture after test, 24 hour curing4hours cure Pb na hthenatm. 1.5 Tra rock W 0 95+ 30/40 40/50 DE 1. 5 go do..... 0. 5 100 70 100 2.0 do an 0 95+ 30/40 80 2.0 ....do -.--d0----- 0-5 100 B0 100 1 After 24 hours cure at 140 F.

In the above table, the term stripping resistance" is defined as the percentage of the a greate surface still-remaining coated with asphalt after the coated mixture has been cured for 4 hours at room temperature and then placed in water maintained at room temperature for a period of 20 hours. The metallic salts that may be used according to this invention are those com- I posed of metals of groups 2 to 8 and division B. of group 1 of the periodic system and are preferably water-insoluble but oil-soluble salts of organic acids.

Although in most cases the treatment of the asphalt with a suitable quantity of lead naphthenate permits its satisfactory application to wet aggregates, especially when the latter are so previously mixed with small amounts of hydrated lime, in certain cases even this treatment does not Lnn: Purmrlo. War Glmm'r Aocsrcsrn Per-cent Treatment in asphalt coated on 2.0% nsphthenic acids mm I claim:

A method of coating a damp mineral aggregate and bonding the damp mineral aggregate as which comprises coating the damp mineral aggregate with 0.5 to 1% of hydrated lime, and adding to the mixture thereby obtained asphalt in fluid condition containing, at the timeof contact with the aggregate, from 1 to 3% of lead 1 naphthenate and 1 to 8% ofnaphthenic acid.

JOSEPH c. aonmcinn. 

